[LLVM-COV] Fix branch coverage merging across function instantiations

[evodius96]

Bugzilla Link	50394
Resolution	FIXED
Resolved on	Jun 17, 2021 10:46
Version	12.0
OS	All
Blocks	#48661
CC	@tstellar
Fixed by commit(s)	eccb925 b89942c

Extended Description

When I made the upstream commit for branch coverage support in code-coverage in January, I made an incorrect assumption that branch coverage numbers (covered branch and total branches) should be accumulated across function instantiations. This is not what is done for lines and regions, where the maximum line/region coverage found in a function instantiation across an instantiation group is returned. For example, if a function template definition has 2 total branches, the branch coverage would be reported as an accumulated total across all instantiations (8 total branches across 4 instantiations).

The correct assumption for the FunctionCoverageSummary::get(const InstantiationGroup &Group, ...) routine is that the summary it returns should agree with the function definition in the source code on lines, regions, and branches. So we should do the same thing for branch coverage as we do for line and region coverage. If a function template definition has 2 total branches, the summary should also reflect branch coverage for 2 total branches.

Code Review for fix:
https://reviews.llvm.org/D102193

Main branch commit for fix:
https://reviews.llvm.org/rGeccb925147d5f262a3e74cc050d0665dd4e6d8db

This fix needs to be applied to the 12.x release branch.

[tstellar]

Hi Todd,

What is your opinion on backporting this?

https://reviews.llvm.org/rGeccb925147d5f262a3e74cc050d0665dd4e6d8db

[tstellar]

Merged: b89942c

[tstellar]

Merged: b89942c

Ignore this, the automation was confused by the revert.

[llvmbot]

I'm OK with backporting this to the 12.x release branch

[tstellar]

What is the final version of the fix that needs to be backported?

[evodius96]

Hi Tom,

The final version of the fix is what I originally reported and tried to merge to the branch before. There haven't been any changes since then. Let me know if that's not what you are referring to.

https://reviews.llvm.org/rGeccb925147d5f262a3e74cc050d0665dd4e6d8db

[tstellar]

Merged: b89942c

[evodius96]

Hi Tom -- I don't yet see this merge on the 12.x branch. The commit SHA looks to be the original commit we did that was later reverted. Not sure if something got mixed up here. Thanks!

[tstellar]

Do I just need to unrevert b89942c to fix this bug?

[evodius96]

Yes, unreverting it should do the trick. Thanks!